In recent years, in order to cope with an increased density and further miniaturization of semiconductor products, a plasma processing unit has been used for manufacturing such semiconductor products to perform processes such as a film-deposition process, an etching process, an ashing process, and so on. In particular, there has been a tendency to use a microwave plasma processing unit that generates a high density plasma by means of a microwave, because the microwave plasma processing unit can stably generate a plasma even under a high vacuum state with relatively a low pressure ranging between about 0.1 mTorr (13.3 mPa) and several tens mTorr (some Pa).
Such plasma processing units are disclosed in JP3-191073A, JP5-343334A, and JP9-181052A, for example. A general microwave plasma processing unit is schematically described below with reference to FIG. 9. FIG. 9 is a schematic structural view of a conventional, general microwave plasma processing unit.
As shown in FIG. 9, the plasma processing unit 102 includes a processing vessel 104 capable of creating a vacuum therein, and a stage 106 disposed in the processing vessel 104 to place thereon a semiconductor wafer W. A discoid top plate 108 is hermetically disposed at a ceiling part opposed to the stage 106. The top plate 108 is made of, e.g., aluminum nitride or quartz to allow a microwave to pass therethrough.
A discoid planar antenna member 110 with a thickness of several millimeters is disposed on an upper surface of the top plate 108 or above the same. A slow-wave member 112 made of, e.g., a dielectric is disposed on an upper surface of the planar antenna member 110 or above the same, so as to shorten a wavelength of a microwave in a radial direction of the planar antenna member 110. A ceiling cooling jacket 114 is disposed above the slow-wave member 112. Since the ceiling cooling jacket 114 has therein a cooling-water flow channel through which a cooling water flows, the slow-wave member 112 and the like can be cooled.
The planar antenna member 110 has a number of microwave radiating holes 116 each of which is, for example, a through-hole of an elongated groove shape. Generally, the microwave radiating holes 116 are arranged concentrically or helically. An internal cable 120 of a coaxial waveguide 118 is connected to a center part of the planar antenna member 110. Through the internal cable 120, a microwave of, e.g., 2.45 GHz generated by a microwave generator, not shown, is guided to the planar antenna member 110. The microwave is radially propagated in the radial direction of the antenna member 110, and is discharged from the microwave radiating holes 116 formed in the planar antenna member 110. After passing through the top plate 108, the microwave is introduced into the processing vessel 104. Due to the introduction of the microwave, a plasma is generated in a processing space S in the processing vessel 104, and the semiconductor wafer W on the stage 106 can be subjected to predetermined plasma processes such as an etching process and a film-deposition process.
When a semiconductor wafer is subjected to a plasma process such as a film-deposition process and an etching process by means of the above-described plasma processing unit, uniformity of the process within a surface of the wafer has to be particularly strictly maintained. In general, with a view to making uniform a plasma density in the processing vessel 104, the distribution or shape of the microwave radiating holes 116 formed in the planar antenna member 110 have been changed (adjusted). However, it is significantly difficult to control behavior of the plasma in the processing vessel 104. Even a slight variation in the processing conditions may give rise to a great change in the behavior of the plasma. As a result, there have been cases in which uniformity of the plasma process within a surface of a wafer cannot be sufficiently maintained.
Recently, a size of a wafer has been enlarged, that is, 12 inch wafers have been used in place of 8 inch wafers, and a further miniaturization and a further reduced film-thickness of a wafer have been promoted. Under these circumstances, there is a strong demand for solving the above problem.